I have been playing with the idea of making a simple, cheap spot welder like a few that I have seen on Pinterest, facebook....ect.
They use a transformer from a microwave, remove the one coil and fit a 35 welding cable into its place. I see that get a voltage of 1,5 volts. On mine I get only 1,3 volts. Why would this be?
I also see that none of them fit a fuse or overload protection to them. Would this be ok if used only for a few small spot welds at a time. I have a few small jobs every now and again when I need something like this. I stripped a trans former and fitted cable and tried it, must say it is quite powerfull. I also need a 2 pole push button switch to switch on the transformer once the work piece has been clamped, any Ideas?

Great idea Roger.Kindly show us a few more detailed photos showing the method you connected the welding cables to the transformer.I have never ever stripped a microwave and don,t know tghe construction of the transformer
Another idea to really fine tune the spot welder is to install a timer to the 220v primary supply which can be triggered by a foot switch or a similar switch.This will control the fusion period of the weld and can then be adjusted accordingly.

Thanks Tony, a person cuts the secondary coil down the one face and hits the rest out with a hammer and punch taking care not to damage the primary coil. The welding cable is fed through the opening left behind. I took a few pics of the voltage when switched on. If a wood screw is turned into one side and then touches it with the other side of the cable, it takes about 5 seconds for it to become red hot. I took a video of it but dont know how to load it. I have read about using a timer but I am not too clued up about this type of work, its all new to me. We will see how and why as we go along.

Interesting. I've seen some you-tube videos before about this but never looked st it seriously since it's something that I would use very seldom if at all.

I'll just wait for Tony to make one and borrow it if the need arises.

When your road comes to an end ...... you need a HILUX!.

Life is like a jar of Jalapeño peppers ... what you do today, might burn your ass tomorrow.Don't take life too seriously ..... no-one gets out alive.It's not about waiting for storms to pass. It's about learning to dance in the rain.And be yourself ..... everyone else is taken!

Ja Andy it will just be a nice to have. I do need one every so often so it would not just sit there. It will not cost very much to make one, I had a transformer and the rest will all be made from scrap that is lying around. Just need something to switch it.

You want to have the control circuit on the 220V side, so get a 220V relay and use that. Don't do the switching on the spot welder side (unless you want to spend $$$$$ on a high current switch). Then use a normal timer or just a momentary switch with a pedal to control it. AC-DC have a good range of switches and a pedal is not difficult to make.

If you can, get nice big copper rod to use as your electrode and turn the ends to a blunt point (no need for a lathe, run the rod in a drill against a bench grinder). Graphite would be better, but it tends to fracture under clamping loads.

The area of the conductor plays a role i.e you could have a thinner cable with more windings or a thicker one with less windings. That crossing there at the rear could also influence the voltage, but I would suggest to stick one end of the welding cable through the core again in other words add half a winding. That should get you close if not a little over.

Just be weary of switching the 220V side, the Txformer could heat up although at the frequency you'll be switching it should theoretically not be an issue. (I've seen this in signage installations where each flashing 12V channel had it's own Txformer and the 220V side was switched; transformers burnt out after a while. I replaced them with one single txformer and swithed the 12v side; haven't had an issue since)

Agree with Nick. Was going to suggest using a 220V bi-pole contactor which is essentially a 220V relay that can carry a 30A load. Then all you need is a small switch or even a bell-push switch to activate it. And as Nick said, install it on the mains side of the transformer.

P.S. For the electrodes you could just use a couple of 8mm copper bolts in your clamp so that they are easily replaceable. The interesting part will be to isolate and insulate the two halves of the clamp.

When your road comes to an end ...... you need a HILUX!.

Life is like a jar of Jalapeño peppers ... what you do today, might burn your ass tomorrow.Don't take life too seriously ..... no-one gets out alive.It's not about waiting for storms to pass. It's about learning to dance in the rain.And be yourself ..... everyone else is taken!